The Internet has widely been used in recent years and users can access various types of information on sites operated all over the world and can obtain such information. Use of devices adapted to broadband access such as ADSL (Asymmetric Digital Subscriber Line) and FTTH (Fiber To The Home) has also rapidly spread accordingly.
Prior techniques relating thereto include techniques disclosed in Japanese Patent Laying-Open No. 2007-036926 (Patent Document 1), Japanese Patent Laying-Open No. 2007-067601 (Patent Document 2), and “IEEE Std 802.3ah-2004” (Non-Patent Document 1). According to the invention disclosed in Japanese Patent Laying-Open No. 2007-036926, a hot optical terminal unit communicates with a plurality of user optical terminal devices through optical transmission paths. The unit has an administrative information storage device for storing administrative information for the plurality of user optical terminal devices. A stand-by optical terminal unit has a storage device capable of storing administrative information transferred from the hot optical terminal unit. A control device controls switching from the hot optical terminal unit to the stand-by optical terminal unit.
In addition, in the invention disclosed in Japanese Patent Laying-Open No. 2007-067601, an L3 switch having a port mirroring function is arranged upstream of an OLT (Optical Line Terminal) and a 2:1 optical coupler is arranged downstream thereof. Prior to start switching, administrative information and setting information are transferred from a first OLT to a second OLT. When a special frame indicating start of switching is input from a switch to the first and second OLTs, the first OLT stops taking in of downstream data and the second OLT starts taking in the downstream data. Allocation of bandwidth to an ONU (Optical Network Unit) is temporarily suspended, the second OLT is instructed to take in upstream data, and allocation of bandwidth to the ONU is then resumed. When there is no down data for the first OLT, administrative information is transferred from the first OLT to the second OLT. The second OLT operates normally.
Further, “IEEE Std 802.3ah-2004” (Non-Patent Document 1) defines one scheme for PON, that is, EPON (Ethernet® PON), under which all information including user information passing through a PON and control information for administering and operating a PON are communicated in a form of an Ethernet® frame, an access control protocol (MPCP (Multi-Point Control Protocol)) or an OAM (Operations, Administration and Maintenance) protocol therefor. By exchanging MPCP frames between a terminal device and a subscriber device, joining, leaving, upstream multiple access control, or the like of a subscriber device is carried out.
It is noted that, in 10GEPON (EPON in which a communication rate is adapted to 10 Gbps) standardized as IEEE802.3av as well, an access control protocol is premised on the MPCP.
Furthermore, Japanese Patent Laying-Open No. 2004-201013 (Patent Document 3) shows that a layer 2 switch (L2SW) is generally used for further integrating upper links of a plurality of PONs. In L2SW, relay processing for each terminal MAC address is performed.
Patent Document 1: Japanese Patent Laying-Open No. 2007-036926
Patent Document 2: Japanese Patent Laying-Open No. 2007-067601
Patent Document 3: Japanese Patent Laying-Open No. 2004-201013
Non-Patent Document 1: IEEE Std 802.3ah-2004